Clinical Reasoning: A 59-year-old woman with multiple myeloma and lower extremity weakness and numbness.

A 59-year-old woman with a history of stage 3 immunoglobulin G (IgG) lambda multiple myeloma (MM) on treatment with bortezomib and dexamethasone, chronic lower back pain, and chronic but improving bilateral lower extremity weakness and numbness presented with 2 to 3 weeks of worsening lower extremity weakness and numbness. Prior to presentation, the patient had been hospitalized for sepsis and cardiac arrest. Weakness affected the left lower extremity before progressing to the right lower extremity, whereas numbness was present in both feet. There was no bowel or bladder incontinence, saddle anesthesia, preceding trauma, or history of radiation therapy. The bilateral lower extremity weakness and numbness resulted in gait impairment and falls, which prompted admission for further investigation. Notably, bortezomib had been started 4 months prior to presentation.